Demodulator device for frequency and amplitude modulation



Aug. 21, 1945. E, H, LANGE DEMODUI JATOR DEVICE FOR FREQUENCY AND AMPLITUDE MODULAT ION' 2 Sheets-Sheet 1 Filed April 28. 1945 fikla u u Min IN V-ENTOR Aug. 21, 1945. LANGE 2,383,323

DEMODULATOR DEvIcE FOR FREQUENCY AND AMPLITUDE MODULATION Filed April 28, 1943 2 Sheets-Sheet 2 ,INVEN TOF? 1 Patented Aug. 21,1945

UNITED STATES PATENT OFFICE. 1

DEMODUIJATOR. DEVICE FOR FREQUENCY ANDAMPLITUDE MODULATION E wa d; H, Lange, Baltimore, Ma. Application A'pril 2 8, 1943, Serial No. 484,937

22 Claims.

This invention pertains to thermionic deg modulator devices for. converting thepattern of frequency-modulation of a. high frequency car riergvoltage' into corresponding output voltages, and more particularly to apparatus for com pensating undesirable modifications introduced or superposed upon; these outputfvoltages by amplitude-modulationof the carrier-voltage;

also for converting the patternof amplitude,- modulation of the carrierf-vojltage into corre-- sponding outputvol'tages. i i

The principal obiect of his invention is to provide such demodulatordevices, employing-a double-diode having a common cathode with two anodes, andIemploying the common cathode with aminimum of other control elements in a single thermionicenclosure, together with simple circuit means, providing these desired functions- Witheconomy of thermionic tubes and of com,- ponent circuit elements; i

A second" object of this invention, is to provide demodulator devices,jemploying a single thermionic tube, and capable of simultaneously providing frequency-demodulation. at one set of terminals andamplitude demodulation at another set of terminals, from an impressed carrier-voltage having both frequency-modulation and amplitude-modulation.

A third objector this invention, is to provide a frequency-demodulator, employingfa, single thermionic tube, andwherein amplitude limita tion isfemployed, and having means for con: trolling the magnitude of the impressed voltage uporrthe limiting device when the output alter,-

nating current of the limiting device falls below the limit set for alternating output currents exceeding thelimit'-value.- i i A fourth object of this inventionis to provide simple frequency-demodulation structures; ca-

pable of yielding output voltages directly proportional to frequency deviation from centre frequency, with zero output voltage at centrefrequency, and'with voltage of oppositepolarities for; frequencies above and below centre-fre j quency; also operable from avariety of mag nitudes of impressed voltage; as distinguished from' aafixedvalue set bva limitation device,

and further", to provide inf said simple struct ures means for compensating the efie'ctof amplitude variations upon the-constant proportion lity between the output voltage of frequency-dd modulation and the frequency deviation from centre-frequencm l A fifth object Ofthis invention is to provide intan amplitude-demodulator having ;a doublediode, with common cathode and two anodesa simple frequency-deviation determining device, providing a positive unidirectional voltage for frequency deviationson one side of a centrefrequency, and negative unidirectional voltage for frequency deviations on the other side, of the, centre-frequency, whereby these frequency-dc termined unidirectional voltages furnish a control means for restoring undesired frequency deviations to a zero value, at the desired centre,-

frequency.

A sixth object of this inventiontis to provide compensation for amplitude-modulation in a,

frequency-demodulator having a doublet-diode with common cathode and two anodes, utilizing a, control voltage derived from the totaliunidirec- .tional current of both anodes; also to utilize this control-Voltage either to modifythefrequency-deviati'on sensitivity of aresonant circuit of the frequency-demodulator, cor altiernatively,, to utilize this control-voltage to determine a cross-modulation in a balanced modulator, having a push-pull amplifier coupled to the resonant circuit.

A seventh, object of this invention, is to pro-,

vide a control-system wherein interconnection between the output terminals for frequency.- demodulation, and the output, terminals, for amplitude-demodulation; is employed to furnish to an interconnected circuit a novel control of currents inthis circuit, utilizinga uni v versal demodulator of this invention.

These objects, and others, are hereinafter pointed out in further detail, and will be better understood by reference to the, drawings, and

to the appended claims;

In the drawings, i

Fig. 1 illustrates a frequency-demodulator, having a thermionic tube containing a doublediodewith common cathode and two anodes, a third anode ,having thermionic conductance with the common cathode, controlledby controlelectrodes, a resonant circuit'and a conductively oonnected choke-coil, the third anode and control-electrodes providing a limiting-* device for the magnitude of alternating \current impressed upon the resonant circuit and (choke-coil The resonant circuit and choke-coil are capacitively gcoupled with the third anode, the frequency- .dernodulator having an output circuit coupled with the resonant circuit, and control means for regulating the resultant amplification of a precedingamplifier, when the alternating current impressed upon the resonant circuit and trodes; also an output circuit for amplitudedemodulation, an output circuit for frequencydemodulation, and control means for compensating the effect of amplitude-variations in a resultant output voltage obtained from the output circuit for frequency-demodulation, the control means including coupling between the third anode circuit and the resonant circuit, for applying a cross-modulating voltage.

Fig. 3 illustrates another universal demodulator, and is a modification of Fig. 2, the resonant circuit being inductively coupled with the principal terminals, and the choke-coil which is conductively connected to the resonant circuit being capacitively coupled to the principal terminals; the control means for compensating the effect of amplitude-variations in a resultant output Voltage obtained from the output circuit for frequency-demodulation, including coupling between the third anode circuit and the resonant circuit, as in Fig. 2, for applying a cross-modulating voltage.

Fig. 4 illustrates a universal demodulator, for both frequency-demodulation and amplitudedemodulation, having principal terminals for applying modulated carrier-currents, a resonant circuit and, conductive-1y connected choke-coil, the choke-coil being capacitively coupled with the principal terminals and the resonant circuit being inductively coupled with the principal terminals, a thermionic tube having a double-diode with common cathode and two anodes, a third anode with thermionic conductance to the common cathode controlled by control-electrodes, an output circuit for amplitude-demodulation, an output circuit for frequency-demodulation, and control means forcompensating the efiect of amplitude-variations upon the frequency-demodulated output voltage, the control means including coupling between the third anode circuit and the resonant circuit, for controlling the resultant conductance of the resonant circuit.

Fig. 1a, illustrates a. conventional thermionic amplifier for applying modulated voltages to the frequency-demodulator of Fig. 1, and illustrates an employment of the control means of Fig. 1 for controlling the voltage-bias of the controlgrids of the amplifier. I.

Fig. 1b illustrates a characteristic of the limiter-device of Fig. 1, and the effect upon the characteristic of increased amplification in the preceding amplifier, determined by decreased negative-bias upon the amplifier control-grids, when the limiter output current falls below its limited value, and illustrates the lower threshold value of signal voltage at which the limit-value is reached.

Fig. 3a. illustrates a type of mutual conductance characteristic for the thermionic tube of Fig. 2 and Fig. 3, and with reference to the third anode, common cathode, and control-grid of this tube, utilized for obtaining a compensating voltage for cross-modulation.

Fig. 32) illustrates a resistance coupled pushpull amplifier for use with the demodulators of Fig. 2 and Fig. 3, and for employment of the compensating voltage for cross-modulation.

Fig. 4a illustrates characteristics of circuit conductance, and superposed thermionic conductance between the third anode and common cathode of the tube of Fig. 4, in relation to negativebias voltage upon the control-grid of this tube, and of total conductance variations necessary for compensating the effect of amplitude-variations upon the frequency-demodulation output.

" Fig. 5 illustrates a circuit interconnected between the output terminals for frequency-demodulation and the output terminals for amplitude- I demodulation, and a control-system utilizing the universal ,demodulators [of this invention, wherein the currents of the interconnected circuit'are determined by both the frequency-modulation and the amplitude-modulation impressed upon the carrier-wave, and applied to .the demodulator.

Referring to Figs. 1-4 of the drawings, at 4 is shown a thermionic tube, having the doublediode consisting of the common cathode 3, with anodes and 2, and having a third anode 5, a suppressor-grid 8, a screen-grid Land a controlgrid 6; the third anode 5 has thermionic conduct ance with the common cathode 3, controllable by the electrodes 6, '1',v and 8. At 32 is a source of unidirectional voltage, the negative terminal of which is connectedto ground, at 44. Connected to anode l, of the double-diode, is the serially connected'high-frequency choke-coil |5 and stopping condenser 5|, and likewise connected to the anode 2 of the double-diode, is the serially connected: high-frequency choke-coil l4 and stopping. condenser 4|, and bridged between the condensers 4| and 5|, is the output resistance I6, such that a circuit consisting of the resistance l6, choke-coils I4 and I5, and condensers 4| and 5|, all in series, is connected between the anodes l and 2. :The'output resistance H5, is by-passed for the high or carrier-frequencies, by the condenser 6| which is connected to ground at 44, Figs. 1 and 4, and by condensers 6| and fila connected to ground 44, Figs. 2 and. 3.

Conductive-1y connected to a resonant circuit,

through a high-frequency choke-coil, is the common cathode 3, of the double-diode, conductively connected through a control-resistance I3; this series connection of cathode 3 throughcontrolresistance I3 is continuous through high-frequency choke-coil 23 to resonant circuit 22-22, Figs. 1 and 2, or through high-frequency chokecoil 23a to resonant circuit i8a,|9w|1, Figs. 3

and 4. Anodes and 2, of the double-diode, are

through resistance l2 to a point q upon reso nant circuit l8a-|9a l1. Resistance v|| is shunted by condenser 2|a,and resistance I2 is shunted by condenser 2|; likewise, resistance I3 i shunted by condenser 3|. Resistances II and I2 are equal. a

. At 9 and ID, are principal terminals for application of modulated carrier-voltages to the demodulator networks; terminal?! is. connected to 2; ceases the positive' terminal of the: source 32 through a high-frequency choke-coil 21, Figs: 1-1 and 2, or through aninductance coil-.26, Figs. 3 and 4'. At

33 and 34'are lay-pass condensers, for respectivelyl-by passing high-frequency currents around the source 32, and for carrying high-frequency currentsuporr the screen-grid 1' directly to: cathode 3, by? a ,low' impedance path. In the demodulators of Figs. 1 andt2; theresonantcircuit 22- -22 and conductively connected choke coil 23, are capacitively". coupled? with the principal terminals,

through condenser 29, Fig". 1, and throu h condensers m and'3,.Fig. 2; in-the'demodulatorsof Figs; 3' and 4'; the resonant circuit l8a- I 9a'l l i is inductively coupled.with the principal tenninals; and 'bhBFChOkB-COH 23:; which is conductively connectedto the resonant circuit l8a-l9afll 1,: iswcapacitively coupled with the principal termi nals', the capacitivecoupling being throughcond'en'ser 28;: and the inductive coupling. being thr'ough mutual inductance between coils26 anfd l8a=-t9d. l i i l Referringnow to Fig.1, the thirdanode 5; su-ppressor=grid B screen-grid T, and control-grid 6, are u'tllized with the common cathode 3, for amplitude-iimitatiori'; there being several wellkn'owrr circuit connections employing these control-elements-to limit the amplitude of high-fre-;

quency signals applied to principal terminals 9,

ll. such: that. beyond a certain threshold value of hfgh f-requency voltage impressed upon the control grid 6,-the signal output will be substantially constant in amplitude, overa large range of input vdltages'; and'such thatxthe subsequentnetwork can be utilized for response. to frequency. devia l tidns,. without the undesired effect of, amplitude variationson this'resporise; For this purpose, input terrninals'flaand Illa are connected to a cone denser 5Bains'eries with a resistance :56, one

terminal of resistance 56 being connected. to the cbritroFgr'id 6 and the'otherterminal of 56 being connected t6 cathode 3; also' suppressor-grid 8 is connected to cathode 3, anode 5 is connected to source 32 through resistanccfl, and screen-grid 1i is connected to a junction between resistances 35 .and. 36 in series, these series connected resistaiices being. shunted. across the. sou-roe 32.

Resistances 35 and 36 are for suitably proportion ing! the unidirectional v'olta'ge u'poir Tl. increlatin td th'ivoltageof 32 a d: likeW iseresistance 3-1 is a for suitably proporti'orii'ng the unidiiectior'iah volt;

p 3 ode," ma manner" well understood: When the modulatedyoltageimpressed uporr Sit-240a is .of'

suificientmagnitude to supply a limited output signal into 9 1 0", throughthe action of the limitin f gdeviceil the voltages present across the: res= onant circuit. 22 22 .;and conductively connected choke-coil 23, arevarieds by frequency deviations. The? resultantalternating voltage across trol-gridsof aprecedingtamplifier, supplying al-z 20m age upon: 5 hrrelati'on. to the voltage" of 32.. It

will b'eundr'stobd that the presentinv'ntion is. not directly concerned. with the connections em; i

played; forlimitatiori of outputfrom anode- 5*,zlout withhthe falling-oft of such output. below. a:

threslidldvale-e er input, voltage, characteristic on 'suchliiniting devices. The impedancekof con-i denser 29 at thehi-gh' orcarrier-frequencies is r negligible in. comparison with that of; the; choke.-

coil23or resonan't circuit 22*22', this condenser. servingsprimarily as a stopping condenser to: keep" voltage of the source 32 from. the diodeanodesi land 2 likewisethe impedance of condensertlo at these frequencies is smal-lfiri comparison with resistance [3:

Condensers 2| and lla likewise temating voltage for" the terminals 3 9a- I 0a, as illustrated in further detail in Fig. 1a. The principles of operation of" the structures, are considered in: furthendetai-l hereafter." H

Referring toiFig: 2, modulated. signals are applied directly to the: principal" terminals 9' |0; there being well knowni' linkag'es for supplying frequency mo'd'ulate'd and amplitude-modulated currents to the" principal terminalsfor example, .utilizingthe source? 32, choke-coil 21 and resist- ;ance 31 for connectiorrtothe anode-cathode of a-pre'c"ed-ing;:high=impedance pentode. In Fig. 2,

operation does not tak'eplaceupon a fixed magnitude' of 1 constantamplitude alternating cur rent, fixed by a:lir'nitati'on device, but permits the" usage of: wide" variety of amplitudes;

.At Mi is a primary winding: of a transformer, and at 41 is a. secondary winding of this transformer; the transfoimer 46'4'I; is forthe low or demodulate'd frequencies'gwthat is, for the frequencies containingthe signal-intelligence;which it is desired to separate from the high or carrier-frequencies. :Avariable resistance 45 is shunted acrosse lfiyandthe' third anode 5 is connected by tli'conductor 49. to apositive terminal of the sourcexiiz' sthe conductor 49 being connected to one terminal of resistance 45, and of winding 46, i

so that variations of current through anode 5 apply a corresponding voltage across primary 46, determined by rsistance' 45, and the current variaticnsimconnected across the output resistance l6, is?v the" primary coil 54, .of a transformer 54:55 for the low or demodulated frequencies.

The secondary '55 l of? this transformer, has a centre-tap O", which is connected. to one terrrninal of the secondary winding 41, the other terminal: of: 41: being connected to ground 44. The

coritrolsgrid :6 is: connected by the. variable-contactor151 to the control resistance I3, whichis have inipedan'ces which are small in==comparisonwith their respective shunted resistances IZv'and' H atpthe carrierjfrequencies; .thus 'each of theparaillelw resistance-capacitance circuits; Iii-31,.

inurelationito the half-period time of the carrier frequencies, capable of smoothing out-th 1 directional voltage across each of these circuits; during w the nonconductive F half-cycle of the diconnectedtothe cathode 3; The suppressor-grid 8 is connected directly to cathode 3 by conductor. 8a.,- and the screen-grid I'is connected by conductor 50 to a positive voltage upon the source 32. Cathode 3 is connectedto ground, at 44, and

shunted across the control resistance I3 is the resistance l3a in series with condenser I312, one

terminal of resistance 13a being c'nnnected to ground lbmdirect connection of this terminal to the terminah of. [3, which. is directly connected with the groundedcathode 3. At 0" and A1, are output terminals for amplitude-demodulation voltages; and. at F1 andFz are. output terminals forconnection .toithe push-pull amplifier of Fig.

3b.,Filbeing connected to terminal H4, and F2 .to terminal= I l5. 3 i

. .Reierring-to Fig, i 3,. low-frequency: transformer and i 434'| is connected in the same manner as in Fig. 2, andlikewise low-frequency transformer 54-55 is connected in the same manner; the secondary is connected to ground 44 at one terminal, and to centre-tap'O" on 55. at the otherterminal, the primary 54-is connected across the output'resistance shunted by variable resistance 45, which is also connected to anode 5 at one terminal and to a positive voltage uponthe source 32 by the other terminaL'through conductor-49. Resistance I3 is likewise shunted by.condenser. l3b in series with resistance l3a, a common terminal of 13a and 13 being connected to the ground 44, the

ungrounded terminal of I3fbeing connected toa terminal of choke-coil "23a; connected to control-resistance l3 by the variable-contactor 5?,and screen-grid 1 is connected to a positive voltage upon the source 32, by conductor 59.. The conductor 8a connects the suppressor grid 8 with cathode 3. The cathode 3 is connected to ground 44, through resistance 42, which is connected across apart-of the voltage of source 32, at the grounded end of 32, and condenser 42a is'connected to ground 44 from the conductor 52, which conductor connects the'cathode 3 to the bias-resistance .42. By this means, a negative bias-voltage can be introduced upon control-grid 6, independent of voltages intro duced upon 6 by control-resistance l3. Terminals O and A1, are for the output amplitudedemodulation voltages, and terminals F1 and'Fz are output terminals forconnection to the pushpull amplifier of Fig. 3b, F1 being connected to terminall I 4, and'Fz being connected'to terminal H5, for obtaining amplified frequency-demodulation output voltages;

Referring to Fig. 4, suppressor-grid 8 is connected by conductor 8a to cathode 3, and screengrid 7 is connected by the conductor 50 .to a positive voltage upon the source 32. The third anode 5, is connected through a tertiary coil 26a to a positive voltage upon source 32, by conductor 53. Tertiary coil 26a has mutual inductance with the resonant circuit |8al9a--l'l, for modifying resistance of l8a' l9al1. A'bias-resistance 42 is connected across a part of source 32, at the grounded end A l, and cathode? 3 is connected byconductor52 to'resistance42. Conductor 52 is connected through condenser 42a1to ground 44. Shunted across a part of the control-resistance 3, at the cathode-connected end of i3, is the primary 40, connected to l3 by the variable-contactor Mb. The primary coil '40 is'a part of the low-frequency transformer 39.40. One terminal of secondary coil 39 of this transformer is connected to ground 44, and the other terminal is connected to the control-grid B. bias-resistance 42, a negative bias-voltage can be introduced upon the control-grid 6, independent of voltages introduced by the secondary 39. The resistance lBa has one of its terminals connected to ground 44, and the other of its terminals connected through condenser 13b to the terminal of resistance I 3 opposite the cathodeconnected terminal of resistance 13. Terminals O and A1, are output voltage terminals for am-- plitude-demodulation voltages, and terminals F1 and O, are output voltage terminalsfor frequency-demodulation voltages.

Having described certain important features of the structures of this invention, other details will be apparent from the following discussion t6, and primary 43 is Control-grid 6 is that the total unidirectional current 'of' both anodes l and 2 of the double-diode, emerges from" the cathode 3 and passes through thecontrolresistance H3. The current through anode I is determined by the magnitude of the vector sum. of voltages across 23 and I3, and through anode 2, by the magnitude of the vector sum of voltages across 23 and l9, Fig. 1 or Fig. 2; likewise'in' Fig. 3 or 4, the current through anode l is deter- I mined by the magnitude of the vector sum of voltages across 23a and 18a, and through anode 2, by the magnitude of the vector sum of volt-H: ages across 23a and-l9a. An important feature:

directly proportional to the amplitudes of the input alternating currents to the demodulator.

networks, and independent of modificationby frequency deviations, for compensating the -un'- desirable effects ofamplitude-variations upon the frequency-demodulation output voltages.

In order to utilize the control-resistance l3 for compensating effects of amplitude variation, it:i's* essential that the unidirectional voltages devel.--'

oped across this resistance are not also modified by frequency deviations employed in. the fre quency-modulation, and for the entire range fo'r which the frequency deviations are employed."

The attainment of this purpose is not inherent in any resistance introduced in the circuit carrying the total unidirectional current of both? the input alternating currents through 22 22 and 23 are constant in magnitude, the total.-

unidirectional current through .13 will,'.in general, vary with frequency deviations. Thefurther conditions eliminating dependence of the By means of of the principles of operation of the devices.

magnitude of total unidirectional currentupon' frequency-deviations from centre frequency, will be apparent tions.

The resonant circuit 22--22', consistsof the variable condenser l'l, together with the-coils l8, l9, and 20. The coils I'B, l9, 20,.can be'separate coils, or a single coil with terminals 221', p, 22, and q. The terminal 22 is located with reference top and q, so that at resonance of the circuit to the centre-frequency, the voltagesacross' p2-2' and across 22'-q, are equal. For a constant. alternating current flowing through 22-22- and choke-coil 23, the voltage across 22-.-22' is'in phase with the current at exact. resonance to centre-frequency, and follows a circle-locu'sfor.

frequency-deviations above and below centrefrequency, and with reference tofthe'constant alternating current. The voltage across 23, is degrees displaced from this current, and at exact resonance the voltages p-22 and 22--q are therefore displaced 90 degrees in phase from the voltage across 22-y, i. e., across the choke-coil 23. When the voltage across 'p22is directed toward 22, the voltage across 22-q is directed away from 22.-' Since the frequency deviations employed are but a small percentage of the carrier or centre-frequency, for the range of deviations employed the voltage across the choke-coil 23 is substantially constant. The'resonant cir'- cuit is however sharply resonant, and the-vdlt from the following considera vassasas 1 ages .p-H and 22:q are dc-phased fromtheir positionat resonance, when the frequency is deviated. 'If forexample, the voltage across122'22' at resonance, is designated :by. Er, and thevoltage acrossthe choke-coil is designatedby Eo and the point .p is at the half-voltage point upon 122-22, then the -.voltages at resonance across voltages across y-parid y q, as the frequency is .LdeVlated on either side of the centre-frequency, are thus readily determined. When E is represented by a vector, then at exactresonance Er/2 "is a vectoriat the tip of E0, and to the rightof E0, --indicating the voltage across gr-2 2, and -likewise avectofEi-Zatthe tip of E0andtotheleftoi Eo,

in opposite phase, indicates the lvoltage q. 22.,

-The loci ofthe voltages across p-22 and q--2 2, "are along circles .of diameter Er-Z, as the frequencyis deviated. Thus at exact resonance; the

i l he unidirectional currents I-through the anodes .el and-*2, are'then equaL and there is no difference of potential between the anodes I and -2 resulting f-ro m the rectified currents. When the frequency "is deviated, -t he voltage y--p is greater than the voltage-y-'q, or vi'cdversafdepending upon tvhther the deviation is positive or negative. The"resultant voltage betweenanodes I and Z, is thus of opposite polarity for positive frequency deviations in relation to thepolarity for negative frequency deviations. i

" 'The total unidirectionalcurrent of both anode l --and 2, which passes throughthe control-resistaance} 13, is determined by the arithmetic sum' of the voltages across y -p-andacross yq, and the variation of this arithmetic sum with frequency deviations, for the entire useful range of such "frequency deviations in the -frequency-n odula- -tion,-mustbe substantially eliminatedin order to utilize the total unidirectional current o'f';both diode-anodes; for compensating efi'edtsof amplitude variations of input alternating currents.

variation, is readily seen to be dependent "upon the ratio-of'Es to -Er employed, that isQupon the'proportibning' of the resonant circuit'in relation to th' volt'age determining factors of the resonant circuit and the conductively connnected choke-coil. Forexamplefif the ratio Eo/E's is designatcdfiy N, the sum of the voltagesaross y 'p' 'and g/ d at resonance is designated by so, 'andthefsumof the voltages across y p and y-'q for frequency deviations "jsuflicient to de-phase .tions will the correspondingly less, howeverfire- .quency deviations capable of \de-phasing by a substantial-percentage of this amount are necessaryto obtain adequate output voltages. A ratio of 1N equal to,w'or greaterlthan 1.00, is'therefore "generally necessary;

" Referring to Fig. 1, la, and 1b, the conductor 51:; is carried to the grids 55,66, and 61 of the amplifier, Fig. 'la, for example, through the respective impedances Z1, Z3, andZs. Cathodes 68,

-69 and respectively of the thermionic tubes :62, 6'3; and 6.4,are Jeach connected-to ground at .144. The anodes of each of the tubes are understoodto be connected to a source of positive voltage,.such as .32, the anode of tube 62 through impedanceZz, the anode o'ftube 63 through impedance Z5, and the anodeof tube through Z7. Impedances Z2 and Ze are understood :to have mutual impedance, likewisetimpedances Z5 and v frequency-modulation is understood to befiapplied Zs are understood to have mutual impedance; signal .voltage having amplitude modulation and toimpedance ,Zl, and impedanceZt is understood to becoupled with the input terminals .9a-l0a, ,of the demodulator, Fig. 1. The control-grids 65, 6,6, and-.61, control thethermionic currents "of the respective ,tubesrfl, 25.3, .and .64, lflOWllhg be-.

tweenthe respective anodesand cathodes of these .of :11., such that when the in utyoltage e aex ceeds a ,;thr.eshold,value indicated .byuTl, varia- .tions of Inno longer take place Withiurther large increases of egn. The above-noted conditions with reference to the ,ratio ,N having been inet, for the resonant circuit :and .conductively connected chgke-coil the; constant current 11. provides through the; operation oftthe double-diode a constant unidirectionaltcurrent in, and a control-voltage at 51a of negativepolarity with reference ;to the ground connectionudd'. This d1, ativ hias vol iae episappliedttothe control- Igrids .5, 66, ,and 61,,and;is.unchanged* for all then the'percentage variations of Soin' relation to a tes are approximately asfollows: When N is Qvariration .is 29.5 percent. when l N. is .1/2, variation is .andwhen Nis 3.00,.variation is 1.0 percent. It ie-therefore evident 1 that by ,employingia ratio .N

tsl ificientlydarge, the effect .of frequency deviagtion uponethe totalunidirectional current can be eliminated. The above illustrationis.given to aid thetter understandina the reflect of frequency viation upon ,the total unidirectional -current, yv enthe input :alternatingcurrent amplitude is constant; it is not: to understood as .otherwise l mitins heidevic s ftthis invent n- :When fre- 1 the .s. e ia 9. .s wer employed, o ma itu .1; 19. er hase helvo tas sg wp esree he pfimentase W na- L voltages ,egn greater than the threshold value, at J1. mWhen hovveventhe voltageegnialls to values less than ,thei-threshold valueiby reason of amplitude nodnlation present upon the signal voltage.,applied;to; Z1,the outputcurrent of thelimiter device 8,115 rbelowthe constantvalue OfIL at 15, and the,negativeebias voltage Ec' upon the i0ptIQ1TgidSq6 5,;,6, and BL is, decreased, increasins 317 resultant. amplification of t the amplifier. fI'he lirnitertcmracteristic is thereby modified; as ,shown a 72, the threshold valuebeing' lowered .to; a pQ itiQn indicated ,by "16. .The equilibrium .c. i ?i9, esult in from such control of the amplifier gbias, ,are, apparent. from the graphs 13, nd lfi each,representingithe amplifier output 3 geegnior, a constant amplifier input voltage t,- z,1,,as tne negative-bias .voltage; .Ec is independentlyhvaried. \The negative blas voltage at ,9, corresponding .to the :constant value of Ir. of line;;-15,' isizhe normal negativeebias, and for the particular input voltage of graph 1:3, .the Lamplivfiei Output Voltage gn for thisznorn'ial bias is in- ,dicated thy (IT- t. whenchowever the negative-- amount n.-s, for the same input voltage.

intersection s of thelimiter characteristic and the bias voltage is reduced, for example to a point s, the amplifier output voltage isgreater by the The amplifier characteristic, determines an equilibrium, wherein the negative-bias voltage produced by the limiting device with control-resistance I3, for the input voltage egn atequilibrium, is exact- 1y equal to the negative-bias Voltage required by the amplifier characteristic to yield this valueof egn. Thus, for the particular constant input voltage upon Zgrepresented by the graph I3, if a fixed negative-bias indicated by 7' were used upon the amplifier, the input voltage upon the limiter would be as indicated by 1-t, and the corresponding limiter output current would be as shown at h, whereas with the bias control the actual input voltage upon the limiter is increased by ns, so that the limiter output current is raised from h to n. Similar equilibrium points i;

are illustrated for the graph I4, for a higher constant input voltage.

The condensers 2|, 2Ia, and 3|, have low im- ,pedance for the high or. carrier frequencies, in

relation to the respective resistances which are shunted, and high impedance for thelow or demodulation frequencies. Choke-coils I4 and I5 are high impedance coils for the high or carrierfrequencies, and have negligible impedance for the low frequenciesof the demodulated voltages, likewise the condensers 4Iv and 5I serve to keep continuous voltage from the resistance I6, and have negligible impedance for the low frequencies. The resistance I6, is thus coupled with the resonant circuit which is connected to the diode- ,nected to ground 44.

nected to terminal H4, and control-grid I06 is trol, the threshold value of constant limiter cur- M rent is lowered, in relation to operation with a fixed negative-bias voltage, and the efiect of am plitude-modulation upon the currents supplied to the demodulator network annulled over tional range, IS-11.

Referring to Fig. 2 and Fig. 3b, the principal terminals 9 and. I0 are understood to be supplied with high-frequency carrier-currents having frequency-modulation and amplitude-modulation;

an addithis is accomplished by well known thermionic linkages, for example :by connection to a. high- 1 impedance pentode, the source 32 serving to energize the anode of the pentode connected to terminal 9, the cathode of the pentode having a connection to ground 44, and the modulated voltages being applied to the control-grid of the pentode. The type of mutual conductance characteristic employed, for the tube 4, and controlgrid 6 in relation to cathode 3 and anode 5, is

illustrated in Fig. 3a, at I8, the ordinates of the plitude.

brought within the range necessary to eliminate -modification of the total unidirectional current of anodes land 2,.fiowing through 'I3, :by frequency deviations, the total unidirectional. current through I3 determines unidirectional .voltages proportional to the amplitudes ofthe alternating currents supplied to the network. By means of variable-contactor 51, upon I3, negative-bias voltageis introduced upon the controlgrid 6. When there is no amplitude-modulation present upon the terminals, 9-,'-,-I 0, but only frequency-modulation, there is no variation of voltage upon control-grid, 6,,and no voltage is transferredfrom primary 46 to secondary 41. -As previously discussed, frequency-demodulation. voltages are then present upon resistanceIG, and applied to the primary coil 54; These frequencydemodulation voltages are amplified by the pushpull amplifier, Fig. 3b, terminal F1 lbein Connected to H4, and F2 to H5. 1 In'Fig. 3b,: tube I0| has control-grid II3, suppressor-grid H0, screen-grid H2, and anode III; tube I02. has control-grid I06,- suppressor-grid I09, screengrid I01, and anode I08. The cathode 1049f tube IOI, and cathode I05 of tube I02, are connected to a positive-voltage terminal of source I03 cat bias-voltage, the negative terminalof I03 being connected to ground 44. Suppressor-grids III) and I09 are connected to the commonCQnnection between cathodes I04 and .I05, screengrids H2 and I0! are connected together, and to the source 32, by conductor 50;and the anodes II I and I08 are connected together 'by two equal resistances 99 and I00 in series, and energized by conductor 49 from source 32,,the conductor 49 being connected to the mid-point of the, equal resistances 99 and I00 in series. Connected to anode III is condenser 95, and connectedto anode I08, is condenser 94. The unconnectedterminals of condensers 94 and 95 are bridged by .the two equal resistances 98 and 9! in series, the

mid-point of this series connection being con- Control-grid H3 is con- .connected'to terminal I I5. Connected to terminal I6, is the phaseinverting connection 96 upon resistance 91. v e

. When there is amplitude-modulation present upon terminals9-I 0, as well as frequency-modulation, the voltage-conversion sensitivity of the frequency-demodulation circuits is modified'and ,this modification must be compensated, otherwise the frequency-demodulation voltages will not correspond in pattern to the original frequency-modulation impressed upon the carrierfrequency. This has been usually accomplished by limiter-devices,- that is by regulating the signal upon the demodulator circuit to a constant amwide range of signal magnitudes, but requires a fixed input to theldemodulator network, fixed by the characteristic of the limiterldevice.

This disadvantage is overcome, in.the demodulators of this invention, Figs, 2, 3, and 4. In Fig. 2,'when the amplitude of alternating currents supplied to 9I0 changes, the voltage upon" control-grid 5 changes accordingly, and also the current through coil 46. The resistance 45 employed, is small in relation to the reactances of coil'46, and the varying voltage applied. to coil'40 is determined primarily by the varying current through 45 The secondary voltage in 41, of the low-frequency transformer 46 -41, is applied to the centretap O" of the secondary 55, tocross-inodul'ate the voltages applied by F1 and Fz'to'thetermi Such usage does not permit utilizing a u I u n u 2,383,823 nalslullland H5 respectively, of the push-pull amplifier, acting as a balanced modulator.- By this means variations introduced inthe voltage across F1 and F2 by amplitude-modulation are compensated the outputivoltages at L92and 83 being frequency-demodulation voltages compensated for the effect ofcamplitudeemodulation.

Amplitude-demodulation voltages .are taken off. at

the terminals O'A1; corresponding tothe voltage variations acrossthe control-resistance l3. 3 In Fig. 3, a similarcompensatingmeans isremployed for compensating the effector amplitude variations upon the conversion sensitivity- 0f the [frequency-demodulator circuit as abovede scribed for *Fig. 2. A fixed negative-bias voltage is provided by connection of cathode 3 to resistance 42, applying afixed'lbias to control-wg ridzfi, inseries with the control voltage applied from resistance l3, by way of circuit 3-42-4244- 413 -51-6; lbiasevoltage gcani bek adjusted to :set-the axis 89 withrefer'enceto whichthe mutual-conductance is modified by voltages from the control-resistance t3, toadjust the relative changes of mutual-conductance "efiected by changes/in amplitude of applied alternating cur rents, above and below an operating .norm. The samepamplifier, :illustratedyin FigFBb, isrconnectedlto Fi and Fawterminal AM. being connected to.,F1,. and terminal M5. to F2; likewise.

amplitude-modulated :and trequencyemodulated alternating currents are supplied to terminals 9-41], as previously. pointed out. i The push-pull amplifier: Fig; i 3b, can: :be used alternatively, tor

amplifying amplitude demodulation, by i connecting terminal =ll4.to A1,,Fig. 2 or Fig. 3,. and by 1':

connecting terminals H5 and l 16 together, tq-apply tovcontrol grid lflfi equalvoltages of. opposite phase tothose appliedtocontrol-grid 1J3,

Referring to Fig. 4,.the frequencyconversion sensitivity; m whereby frequency deviations ,are

converted into output voltages, is compensated has one ,terminal oconnected. $0 the control-grid- G, and the other terminal connected togg round 44.; Cathode 3 is connected by conductor 5 2,to. biasrresistance 42, negatively biasing the control-grid 6, by way of the, circuit 3-52-4 2-44 39-6. Anode 5 is supplied with-positive v l a e :fmm t e sQurce r u tertiary coil 26a and conductor 53', the tertiary cbifZfia-beingcoupled by mutual inductance with inductance ltd-ma.- The polarity r voltage ap li o -gri fish h lseeend r .3 1: is tutu that lwiienthe unidirectional current throughi l ii increases through corresponding int-1 crease of, alternating current amplitudes of the highfirequencysupplied to 9- 0, the. vo t ofthe 'natura'l resistance-of the resonant circuit, and between line Bland the dottedline 8lw re indicated various values of conductance between anode 5 and cathode 3, designated by g and in relati'on'torvarious values of negative bias voltage upon control-grid 6. At88 .is indicated a resultant conductanceflg, of both the conductance go and a for afixed negative-bias voltage.

indicated by -Ec. By adjustment of the part of resistance shunting the primary 4B, em-

ploying 51b, the variationvoltages introduced upon control-grid 6 by/secondary coil 3 9, can

be made tofmodify the resultant conductance in proper relationship to variations'of amplitude of the high-frequency currents applied to 9-10, to maintain constant conversion sensitivity of the network tofrequency deviations. When fthere is no amplitude-modulation present upon terminals 9- -10, but only ire-i quenoy-rnodulation, the total unidirectional current through I3 is constant, the previously discussed proportioningfoi the voltage ratio N for choke-coil 23a and resonant circuit l8a-I9a l1 having been carried outythereis then no variation voltageapplied to the control-grid 6, and nomodificationof the resonant circuit other thanth'e couplingwith it of a constant thermionic;conductance,-between Stand, 3,

As previously dis-cussed, frequency [deviations r from centre-frequency unbalance the currents of anodes l and Land establish voltage differ encesacross I and 1 3,1; between the anodes l and 2,. which .are transmitted to the output-resistance 16 and to terminals F1 and 0' thereof .0 being connected. to ground .44. Amplitude- A1, the resistance l3a being cdupled lwith l3 thrq ea co den 12 n .4 w i h J andensers ,have, low impedance for the low or; demodulation frequencies. a, In order to aid in a better understanding of the principles employed in the compensating systemof cross-modulation, Fig. 2 or Fig. 3, and Fig. 3b, and inithe system of compensation by conductance control, 4, certain useful re lationships are hereafter pointed out, with the understanding, that these relationshipsare not tube-construedflasany manner of limitation uponthe employment fore disclosedl 1 i impressed by 39 uponB will increase the con:

ductance between anode 5 andjcathodeh Fig. 4a. illustrates ,certain conductance relationships; withreference to the ;axis 81 along which conductance is measured, and the axis 82 along Which-negative-bias voltage on 6 is measured. At 90 isa line indicating the constant conduct ance :w-hich is the tertiary shunt equiva-lent of' the structures hereto -In the demodulator networks,- employing. a resonant circuit "and conductively. connected choke-coil to apply alternating voltages toa double-diode, the 9 difierential-voltage developed as a result of frequency-deviation 1 from a centre-frequency for which-the resonant circuit is tuned, is readily determined intermsof the magnitude of frequency deviations; the. conduc tance of the resonant circuit, and the amplitude of lhigh-frequenoy alternatingcurrents supplied.

to the network; thus if the differential voltage developed between anodes l and 2, designated bytEr, and the resultant shunted conductance:

of the tertiary circuit by g xand the amplitude of Q the. alternating currents by Ia,.then: u

u magma/g t (1) in which K is a constant coefiicient, and JAfHthe magnitude of frequency deviations from centre-' frequency. In the system employing .crossmodulation, the conductance of the resonant circuit constant and this relationship lean-he;

in whichK is a constantcofiicient. Inna? demodulation is taken ofi. at terminals 0 and 2' or 3, the part of this voltage applied to each control-grid of the amplifier Fig; 3b is Ef/Z, that is, half of the voltage is applied from O to F1, and half from F2 to O". The compensating voltage applied by the secondary 4.! is designated by 6a, and the resultant voltage applied to one of the control-grids of Fig. 3b is thereforez.

elk-EH2 and the resultant voltage applied to the other control-grid of Fig. 3b is: ,v

I ea+Ef/2 V The mutual-conductance characteristics of the tubes fill and I02, are substantially identical, andstraight line relationships with negative-bias voltage over the operating range used, therate tive when the alternating current Ia increases above a norm, zero-when the current Ia is equal to the norm, and positive whenthe' current Ia falls below the 'norm, in order to provide operation equivalent to that of operating with a constant alternating current norm Ian: This requires:

The control-voltage produced atresistance placed upon 6 by the voltage across-51944, is directly proportional to the amplitude of alternating currents supplied to, 9-l8.. Designating this ,control-grid'voltage as Ego for the corresponding norm Iao .of alternating current, and as Eg for the corresponding current Ia which is variable above and below Iao, then:

' Ego/ Eg=Ia o/Ia v also, the compensating voltage ea is directly; pro-. portional to the variations of current through anode 5 to cathode 3, designated as z' sothat ed=K2i K2 being a'-'constant coefficient. In view of these relations, the required equality of, Equation 5 is converted to: '5 o indicating the type of characteristic between control-grid negative-bias voltage and plate cur I rent to anode 5, required, the coefficient K: takinginto account In, and K2, and a constant value of Ego. The typeof mutual-conductance characteristic is readily determined from (6).

In the system of compensation employed in Fig. 4, wherein a resultant conductance is modified in relation to the magnitudes of high-fre- "ductively coupled-with the resonant circuit is two-foldin its effect. The conversion sensitivity is determined by the product of two factors: the

magnitude of the voltage across the resonant circuit. which is conductively connected to the choke-coil and double-diode, and the rate at which the voltage across this resonant circuit is .de-phased from its resonant value by frequencydeviation; each of these factors is readily shown to be inversely proportional to the resultant conductance across the tertiary coil, the conversion sensitivity thus being inversely proportional to the square of the resultant conductance across the tertiary coil. Referring to Fig. 4a, there is illustrated at 9| a parabolic curve with reference to origin 02, removed from origin 01 of nega tivebias voltage, by an amount of negative-bias indicated by .Eco. This curve indicates a constant ratio between resultant conductance quared, that is g and decreasing negative-bias, such that (ECOEC) /g is constant. As indicated by Equation 1, constant conversion sensitivity requires a constant ratio Iii/g The resultant conductance g is indicated in relation to negative bias,by the ordinates. between 82 and 81, when a characteristic such as 8'! is employed for cathode-anode conductance 3-5; such characteris-. tics are common in conventional thermionic tubes. It will be noted that a high degree of conformance exists with reference to the parabolic curve 9|, and over a wide range of bias-varia-, tions about an operating conductance such as indicated at 88. Changes in negative-bias upon control-grid 6, are effected in proportion to changes in amplitude of alternating currents L with reference to a norm Ian. By adjustment of 51b upon control-resistance l3, variations of negative-bias voltage upon 6 in relation to a fixed bias voltage can be adjusted, and compensation efiected for a wide range of arrier'amplitudes, each having a large amount of amplitudemodulation. v 1

- It will be evident; that a coil such as 26a. can be coupled inductively with the resonant circuit 22-22 of Fig. 1, transformers 46-41, and 54-55 being dispensed with, and transformer 39-40 being similarly employed, as in Fig. 4, .to control the negative-bias voltage upon control-grid 6. The coil 26a through which anode 5 is then connected, acts similarly to modify conductance of the resonant circuit 22 -22, to compensate undesired effects of amplitude-variations in chang ing the conversion sensitivity of thecircuit.

Referring to Fig. 5, an external circuit indicated by impedance Zaf is connected by variablecontactors H1 and H8 to the impedances Zrand Za respectivelih, impedances Zr and Z9. being connectedjin series, and having their common connection 0 connected to ground 44. 'Z: is an output impedance for frequency-demodulation, such as l6, Fig, 4, or either 91 or 98, Fig. 3b. Zais an output impedance foramplitude-demodul'ation', such as l3a, Figs. 2, 3, 01'4. The relative magnitudes of' voltages of frequency-demodulation and of amplitude-demodulation impressed upon Zn are adjustable by the c'ontactors H1 and I18, respectively. When the impedances Z: and Z3, are a part of one of the universal demodulators of this invention, as above noted, e. g.,

. Fig. 4, or Fig. 2, Fig. 3, and. Fig. 3b, control of the currents in Zaf is effected simultaneously by both'the frequency-demodulation voltages and the amplitude-demodulation voltages. As an example of such control, when a high-frequency carrier is impressed upon thedemodulator, havthe control-grid ofthe high-impedance pentode.

"ing both-ai'nplitude-moduiation and frequency I In Figs. 1 and 2; the impedance of the circuit modulation; if; both theamplitu'des and the frequency of the carrier are modulatedby the same [low frequency, then the vector sum of voltages in 'Zar is'controlled by the phase-shift of the low frequency modulating the carrier "frequency inrelation to the same low frequency modulating the carrier amplitudes, If for example, the voltagesof Zr and Za are adjusted to equality-by Ill and H8, then all magnitudes of, voltages from zero-to twice either of these voltages; are attainable upon Zaf, and controllable,by appropriate control of this phase-shift in the transmitted carrier. l

In Figs. 2, 3, and 4,'the third anode 5, and con trol-grid 6', screen-grid l and suppressor-grid 8 are employed with the common cathode 3, for *compensating variations of the proportionality through coil 21 and resistance 3l, is also high in "relation tothe impedance of 22-22-23.

Having described several illustrative embodiments of my invention, it will be evident that changes can be made in the form andarrangemerit of parts, and by substitution in part of 'other well-known structures, without departing from the spirit of my invention, as set forth in the appended claims, and I do nottherefore limit the scope of the invention to such-particular ernbodimentsflor otherwise than by the terms of of frequency-demodulatedvoltagesto magnitude of frequency deviations from centre frequency, caused by amplitude-variations of the high-frequency carrier currents; this compensationis es sential when it is necessary to reproducea pattern of modulated carrier-frequency in the frequencydemodulation voltages. When however, it is required to provide only amplitude-demodulation,

together with means for yielding a positive control-voltage for frequency deviations on one side of the centre-frequency, and a negative controlvoltage for frequency deviations on the other side of the centre-frequency, for example for use in frequency stabilization, then the connections to the anode 5, suppressor-grid 8, screen-grid ,1 and frequency are provided upon resistance [6, connected between the choke-coils]; and I5.

the appended claims. 3

What is claimed is: i

1.- In a demodulator-device, a thermionic tube having a' doublediode with a first anode, a second anode, and a common cathode, a resonant circuit includingan inductanceeoil, a tuning condenser connected across said coil, and connections between a first terminal anda second terminal upon said inductance coil, said connections including afirst resistance connected from said ,first terminal to said first anode, a second resistance connected from said second terminal to said second anode, a third resistance bridged between the first and second anodes,said bridge including a serially connected first choke-coil and condenser between the first anode, and one terminal of said third resistance, and a*seria1ly connected second chokecoiland condenser between the control-grid -6, can be dispensed with; these contrdl-elements are then made available for other uses, only the common cathode 3,- anodesel and 2 being required. Amplitude-demodulation is then provided acrossA1-O', and control voltages responsive to 'frequency deviation from ,centresecond anode and the other terminal of said third resistance, and condensers shunted across each or said resistances; a thirdchoke-coil conductively connected from a third terminaluponsaid inductance coil at the half-inductance point bei I tween said first and second, terminals, to said cathode, and a ground connection to said. cathode. I

l 2. In combination with the structure ofclaim 1, a1control-resistance in series with said third In Fig. 1, condenser 59 serves to further r educeany voltages of carrierJre uency present upon 51a to a negligible value, without effecting the response upon 51a to low frequency ,variations of bias when the limiter output falls below its limit, by reason modulation. l M h "It will be evident, that demodulator networks of the type illustrated in Figs. '3 and 4, can equally well be utilized with the limiter-device of Fig. 1,

of low frequency amplitude that is, theconnection 5117. can be similarlyem ployed to regulate the bias ofya preceding amplichoke-coil, between the cathode and said third choke-coiL and a condenser connected across said control-resistance. l l

3. In combination with the structure of claim 1, a third anode and a control-grid in said therfier from control resistance I3 of this type of circuit, the compensating meansof Figs. 3and 4 being of course omitted, and the anode] 5, suppressor-grid 8, screenegrid 1, and control-grid 6 being connected as in Fig. 1., In Figs. 3 andd l,

inductance coil 26 is tuned to jthe' centrerfree quency by condenser 25, in like manner to inductance coil Ma-49a, tuned by condenser H.

The centre-tap at 220) is understoodt provide likeanionic tube, said control-grid controlling ther- -mionic conductance between the third anode and common cathode, a control-resistance ,in" series with said third choke-coil, between said cathode and a terminal of said third choke-coil, a source of unidirectional current with negative terminal connected to ground, a first coupling means coupling said eontrol-grid with said control-resist ance, and asecond couplingmeans coupling said 1 third anode with a positive terminal upon said source, and with said resonant circuit.

wisethe previously discussed voltage ratio'LEQ /Er,

to apply to the ratio of or i, aresuppliedfiom a high-im edance jpen tode; the input impedance of thenetworks isvery small in comparison with the andde cathojde variation resistance of thepentode, and changes ofi-riput im-pedance are also very small in re1 a- 4. A demodulator-device,"having a thermionic tube containing a double-diode with a first anode, a second anode and a common cathode, and containing a third anode and a control-grid con: 1 trolling thermionic conductance between said third anodeand common cathode, a resonant circuit including connections to said first and second anodes and a first output-impedance connected between the first and second anodesya choke-coil conductively connected from saidresonant circuit to said cathode, a control-resistance serially connected between said cathode and tion--to this resistance; the alternatingcurrents supplied to] the networks are thus substantially constantin proportion to the-voltages applied to said choke-coil, a ground connection to said cathode; a source of unidirectional current having the negative terminal connected to ground, a

second output-impedance connected to said control-resistance, a first coupling means coupling said control-grid with said control-resistance, and

a second coupling means coupling said third anode with a positive terminal upon said source and with said resonant circuit.

5. A demodulator device, having a thermionic tube containing a double-diode with a first anode,

a second anode, and a common cathode, a third anode, and a control-grid for controlling thermionic conductance between said third anode and the common cathode, a resonant circuit having connections to said first and second anodes and an output-impedance bridged across said first and second anodes; a choke-coil conductively connected between said resonant circuit and said cathode, a control-resistance serially connected between .said choke-coil and said cathode, a ground connection to said cathnant circuit and conductively connected chokecoil for frequency-deviations, effected by amplitude-variations of carrier-currents, said compensating means including coupling between said control-resistance and said control-grid.

6. In a demodulator-device for demodulating amplitude-modulated or frequency-modulated high-frequency alternating currents, a thermionic tube containing a double-diode with a first anode, a second anode, and a common cathode,

a resonant circuit having a connection to said first anode, a connection to said second anode, and an output-impedance for frequency-demodulation bridged between said first and, second anodes, a choke-coil conductively connected between said resonant circuit and said cathode, a

ground connection to said cathode, coupling means for coupling said resonant circuit and choke-coil with a source of modulated high-frequency currents, and a control-resistance serially connected between said choke-coil and said cathode, shunted by capacitance, providing a unidirectional control-voltage upon said controlresistance, independent of frequency-modulation, and proportional to the amplitudes of said alternating currents.

'7. In combination with thestructure of claim 6. a third anode, a control-grid, a screen-grid, and a suppressor-grid in said thermionic tube, said grids controlling thermionic conductance between said third anode and the common cathode, and connections of said grids and third anode to said cathode, including a coupling between said control-resistance and said controlgrid, compensating undesired modification of the differential-voltage sensitivity of said resonant circuit and connected choke-coil for frequencyd-eviations, effected by said amplitude-modulation.

8. In combination with the structure of claim 6, a third anode, a suppressor-grid, a screengrid, and a controlgrid' in said thermionic tube, said control-grid controlling thermi- .to said third anode, and compensating means cuit and connected choke-coil to frequency deviations, efiected by said amplitude-modulation, said compensating means including coupling between said control-resistance and said control grid. l

9. A demodulator-device -for frequency-demodulation and for amplitude-demodulation, having a thermionic tube containing a doublediode with a first anode, a second anode, and a common cathode, and containing a third anode, a suppressor-grid connected to said cathode, a screen-grid, and a controlgrid, said grids controlling thermionic conductance between the third anode and saidcathode, a source of unidirectional voltage having a negative terminal connected to ground and to said cathode, an output circuit including a resonant circuit, connections from said resonant circuit to said first anode and to said second anode, a choke-coil conductively connected to said resonant'circuit and serially connected through a control-resistance to said cathode, a condenser shunted across said control-resistance, and a first output-impedance coupled with said first and second anodes; a second output-impedance coupled with.

ulation, said compensating means includingtheconnection of said screen-grid to a positive terminal of said source, the connection of said third anode to a positive terminal of said source, coupling between the control-grid and said controlresistance, and coupling between said thermionic conductance of the third anode and said output circuit. s

10. In combination with the structure of claim 9, a common ground connection upon said first onic conductance of said third anode with said common cathode, a connection between said suppressor-grid and saidcathode, said'coupling means including a source of unidirectional volt: age having a negative terminal connected to ground, a positive terminal connected to said screen-grid, and a positive terminal connected output-impedance and .upon said second output-impedance.

11. In'combination with the structure of claim 9, circuit means connected to said first outputimpedance and to said second output-impedance, for combining frequency-demodulation voltages and a mplitude demodulation voltages V 12 A demodulator device for demodulating high-frequency carrier-currents having frequency-inodulation and amplitude-modulation, havinga thermionic tube containing a double-diode with a first anode, a second anode, and a com-, mon cathode, and containing a third anode,- a suppressor-grid connected to said cathode, ,a screen-grid, and a control-grid, said grids con: trolling thermionic conductance, between the third anode and cathode, a source of unidirectional voltage with a negativeterminal connected t ground and to said cathode, an output circuit including a resonant circuit, connections from said resonant circuit to said first anode, and tosaid second anode, a choke-coil conductively connected to said resonant circuitand serially connected through a control-resistance to said first outputimpedance, f or modification: of who differential-voltage sensitivity to frequencwdevie ,ation of the resonant circuit and choke coilyby said amplitude-modulation said, compensating means including the connection of :said' screengrid to a positive terminal of: said. source, the connection of said third-anode to a positive 'terminal of said source, coupling between the, control-grid and, said i control-resistance,"and coupling between said thermionic conductance the third anode and said outputxcircuit: 13,, In a d'emodulating devicefiorudemodulatin frequency-modulated alternating currents thermionicdouble-diode, means having a firstianode, a secondanodeand a common cathodaresonant circuit means; including an inductancecoil for determining alternating Voltages 1 responsive to frequencies of said currents andre'sponsive to amplitudes of saidcurrentsa connectionyfrom said firstanode to a terminalqof, said inductance coil, through a first resistance, a connection from said second anode to a'second terminal upon said inductance coil through a second resistanceequal ages, and compensating means for compensating the frequencyedemodulation voltagesvupongsaid tosaid first resistance, acondenser shuntedacross said first resistanca-ja "condenser'shuntcdracross said second resistance, a connection from'the half-inductance point upon said, inductance coil between said terminals to said common cathode,

including a conductive impedance carrying the total thermionic current of bothsaid anodesand having a large time-constantin comparison-i with the half-cycl pericdof said alternating currents,

and filter means connected between said'resistrances, includingwan utput-resistance for frequency-demodulated voltages.

, 14. A demodulator for demodulating ea quency-modulated alternating currents, said domodulator having thermionic double-diode means with a first'anode, a second anode, and a common cathode, resonant circuit means including inductance coil means for determining alternating voltages responsiveto frequencies of said currents and responsive to amplitudes of said ages responsivefto frequencies. of said carrier currents, a conductive impedance having a. low

Power-factor atsaidcarrier frequencies, a connection from said first: diode-anode through a first resistance toa terminal of saidinductance coilimeans, aconneo'tion from said second diodeanode "through a second resistance equal tosaid first resistancegto a second terminal upon said inductancecoil means, a connection from an intermediate: terminal upon said inductancencoil means between said terminals to said common cathode including. said conductive impedance, filter means connected between said diode-anodes including an output-resistance, for frequencydemodulated voltages, and-means for impressing said; carrier currents] upon said resonant circuit 1 means including said control-gridand coupling :between; said resonant circuit third, anode. i

16, In combination with 15, a: thermionic amplifier having an output-im-j pedancecoupled with said control-grid, and; a connection-between grid control means ofsaicl amplifier andcathodes of said amplifier including ,awcircuitvthrough a part of said conductive impedance.

;17 In combination with the structure of claim 13; a compensatingmeans for compensating variations of the amplitude factor of said alternating currents ,modifying said frequency-demodulated voltages, said meanshaving a controlcircuit inance H ,cluding a path through said conductive imped- H ,18. In areceivin g system for frequency modulation and amplitude-modulation, a demodulator device providingsimmtaneous frequency-demodul-atedvoltages and amplitude-demodulated .voltages, said device including a thermionic tubehaving a double-diode with a first diode-anode, a second diode-anode, and a common cathode, a

, third anode, and a control-grid for controlling currents, a connection from said first anode to a terminal of said inductance coil means through a first resistance, a connection from said second anode to a second terminal upon said inductance coil means through a second resistance equal to said first resistance, a connection from an intermediate point upon said inductance coil means between said terminals to said common cathode,

total thermionic current of both saidanodes and including a conductive impedance carrying the having a large time-constant in relation to the eluding a first diode-anode, a second diode-anode, and a common cathode, a third anode, and a control-grid for controlling thermionic currents 'betweensaid common cathode and said third anode, resonant circuit means including inductance coil meansfor determining alternating voltthermionic currents between said common cathode and third anode, resonant circuit means determining alternating voltages in relation to said amplitudes and frequencies, connections between said resonant circuit means and said double diode including a conductive impedance connected from said common cathode to said reson-ant circuit means, carrying the total thermionic current of both said diode-anodes; a first outputimpedance for frequency-demodulated voltages, coupled with said first and second diode-anodes, K a second output-impedance for amplitude-de modulated voltages coupled with said conductive impedance, a common connection between said output-impedances, compensating means compensating said frequency-demodulated voltages for amplitude-modulation upon said resonant circuit means, including a control-circuit connected through said conductive impedance to said control-grid and circuit connections to said third anode, and a third output-impedance connected between said first and second outputimpedances for currents determined by both said demodulated voltages. l e 4 19. In a demodulating device for demodulating frequency-modulated carrier-frequency voltages,

resonant circuit means including inductance coil means for determining alternating voltages I recarrier-frequency voltages, a first voltage-rectifymg means including a first thermionicfidiode sponsive to frequencies and to amplitudes of said means serially connected with a first resistance,

second voltage-rectifying means including a sec-] ond thermionic diode means serially connected means and said the structureoffclaim l A "ent of frequency-modulation,

with a second resistance equal to? said first .re-

sistance; a junction between the negativerectifled-voltage terminals ofsaid voltage-rectifying means, a connection from: a'terminal of'isaid inductance coil means to the terminal: of said first rectifying means opposite said junction, a

. connection from a secondlterminal upon said inductance coil means'to itheterminala-of said second rectifying means oppositefsaidnjunction, a connection from said ju'nctionto an intermediate terminal upon said inductance" coil means between said" I tenminals thereon, includinga third resistance shunted bya condenser,

"carrying the sum total thermionic: currents of .both diode means; thermionic amplifying means coupled with saidresonant circuit meanswfor energizing said resonant circuit means with carrier-frequency currents, including a-control-grid means for applying said frequency-modulated carrier-frequency voltages, and acoupling means with said frequency-modulated alternating voltages, "including a thermionic amplifyingmeans coupled with said resonant circuit means and having a contfrol-grid means for applying "said frequency-modulated voltages, "and a:--"co'up1ing means coupling said resistance with said controlgridrmeansyfor maintaining a constant'ratio of conversion of frequency-deviations intooutpllt voltages-independent of amplitude variationsof said .alternatingvoltages. I 1 .21; A frequency-demodulator device" for -demodulating frequency-modulated 1 carrier eurrents, said device-having a thermionic double diode with a first-anode, a second anode; anda common cathode, resonant circuit means incli iding inductance coil-means for determining 'al ternatingvoltages responsive to said frequencies, a connectionfrom a terminal of said inductance coil means: to said first anode through a first resistance, a connectionfrom a second t'e'i'mirla'l uponsaid inductance coil means to said second anodeithrough a second resistance equal to said first .resistance, a:connection from an intermediate terminal upon said inductance 'coil means between said terminals to' said common cathode, carrying the total thermionic current of both saidano'des, an output-impedance'for frequency=demodulated voltages, andconnections between said resistances including said-outputimpedance and a filter-means.

22. In combination with the structure of claim '21, said connection from said intermediate ter- 

